Hydrogen storage materials show considerable benefits in volumetric efficiency over simple pressurized storage tanks These materials typically span a wide range of required operating pressure-temperature conditions which are necessary to achieve their maximum hydrogen storage capacity. For example, sorbents typically call for storage at cryogenic temperatures (e.g., 77 K) whereas complex and chemical hydrides rely on heating (to as high as 600 K) to facilitate hydrogen release. The U.S. Department of Energy set a 2010 goal to achieve an approximate 3-minute refuel time for these hydrogen storage materials, in an effort to match conventional gasoline tank fill times. On the other hand, a minimum full-flow rate (for hydrogen release) of 0.02 (g/s)/kW is typically required for proper fuel-cell operation. During the hydrogen recharging, a significant amount of heat has to be extracted, while the appropriate amount of heat has to be supplied to generate proper hydrogen desorption rate. Thus, efficient cooling/heating of the storage device to match the optimum operating temperature (along with facile inherent material kinetics) of a given storage material is essential to meet these requirements. This drives the need to characterize the engineering properties (such as, for example, capacity, kinetics, thermo-conductivity, cyclability, impurity effects, etc.) of various candidate hydrogen storage materials, particularly in combination with various associated heat exchanging structures.
Interfacial heat resistance and thermal conductivity may be important engineering properties to characterize for any devices in which heat generation and transfer tend to limit the rate of the concerned processes, such as the rates of hydrogen absorption and desorption for a given hydrogen storage material. Conventional thermal characterization techniques complying with ASTM D-5470-06 typically employ a pressure vessel containing a single storage material, and a heat exchanger (including fins and coolant tubes) running through the sample material. In such systems, the heat resistances from three interfaces (materials-heat exchanger, materials-vessel, and materials-coolant tube) are typically measured. Operating this type of test system presents certain challenges. First, heat-resistance data for the material and heat exchanger is confounded with data from the material-vessel and material-coolant interfaces. Thus in order to isolate the thermal information for the desired material-heat exchanger interface, one may need to perform tedious calibration and data processing in order to subtract out the effects of the other two interfaces. Second, the structure of such pressure vessel test setups typically allows only one storage material and heat exchanger combination to be measured at a time. Third, the measurement process used with such systems tends to be costly and challenging due to the large amount of sample material required to fill the vessel and the time-consuming manner in which the sample is typically loaded and packaged.